Method for measuring high-temperature light-induced degradation and method for predicting the rate of output degradation of solar cells

Abstract

To provide a method for measuring high-temperature light-induced degradation and a method for predicting an output degradation rate of a solar cell that can reliably separate an effect of BO-LID from LeTID.SOLUTION: A method includes a first light soaking step of injecting carriers into a p-type crystalline silicon and maintaining the p-type crystalline silicon at a temperature of 50°C or more and 150°C or less until the p-type crystalline silicon reaches a regenerated state, a first measurement step of measuring a first deterioration amount of p-type crystalline silicon in the first light soaking step, a dark annealing step of heat-treating the p-type crystalline silicon at a temperature of more than 150°C and not more than 250°C, a second light soaking step of injecting carriers into the p-type crystalline silicon and maintaining the p-type crystalline silicon at 50°C or more and 150°C or less until the p-type crystalline silicon reaches a regenerated state, a second measurement step of measuring a second deterioration amount of the p-type crystalline silicon in the second light soaking step, and a calculation step of calculating a high-temperature light-induced deterioration amount of the p-type crystalline silicon by using the first deterioration amount and the second deterioration amount.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for measuring high-temperature light-induced degradation and a method for predicting the output degradation rate of a solar cell. [Background technology]

[0002] The light degradation phenomenon of solar cells is generally known as LID (light-induced degradation). One of the LID phenomena, LeTID (light and elevated temperature induced degradation), is a type of degradation that is currently a problem in mainstream p-type crystalline silicon PERC cells. However, the root cause of LeTID degradation has not yet been clarified. In order to minimize the impact of LeTID degradation, it is important to clarify the mechanism of LeTID. And in order to clarify the mechanism of LeTID, it is important to quantify the loss due to LeTID.

[0003] In Non-Patent Document 1, as shown in FIG. 1, in order to separate the effects of BO-LID (boron-oxygen complex-related light-induced degradation) from LeTID, the temperature of the cell or module is kept at about 25°C before the LeTID test. Then, a current close to Isc is injected or light is irradiated. At this time, a stabilization process for BO-LID is performed for a period of about one day to one week. This utilizes the difference in the temperature range in which LeTID and BO-LID occur. While LeTID is prominent at temperatures of 50°C or higher, BO-LID can occur even at a temperature of 25°C. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] F. Kersten, M. Pander, M. Koentopp, M. Turek, W. Bergholz, T. Pernau, Towards a Test Standard of Light and Elevated Temperature-Induced Degradation, PV-Tech, London 2020. Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the conventional BO-LID stabilization process for separating the effects of BO-LID from LeTID, the sample is heated by Joule heat due to current injection or light irradiation. As a result, the temperature of the sample may reach 25°C or higher, which may cause LeTID. As a result, there is a problem that LeTID and BO-LID cannot be accurately separated. Furthermore, due to this problem, there is a problem that the aging light degradation phenomenon of solar cells cannot be separated into LeTID and BO-LID and predicted with high accuracy.

[0006] The present invention has been made in consideration of the above problems, and aims to provide a method for measuring high-temperature light-induced degradation that can reliably separate the effects of LeTID and BO-LID, and to accurately predict the aging degradation rate caused by the photodegradation phenomenon of solar cells, taking into account the temperature dependence of LeTID and BO-LID and the degradation behavior over time. [Means for solving the problem]

[0007] In order to solve the above problems, the present invention provides the following means. (1) One embodiment of the method for measuring high-temperature light-induced degradation according to the present invention comprises: a first light soaking step of injecting carriers into the p-type crystalline silicon and holding the p-type crystalline silicon at 50° C. or higher and 150° C. or lower until the p-type crystalline silicon is in a regenerated state; a first measurement step of measuring a first deterioration amount of the p-type crystalline silicon in the first light soaking step; a dark annealing step of heat-treating the p-type crystalline silicon at a temperature higher than 150°C and lower than 250°C; a second light soaking step of injecting carriers into the p-type crystalline silicon and maintaining the p-type crystalline silicon at 50° C. or higher and 150° C. or lower until the p-type crystalline silicon is in a regenerated state; a second measurement step of measuring a second deterioration amount of the p-type crystalline silicon in the second light soaking step; and a calculation step of calculating a high-temperature light-induced degradation amount of the p-type crystalline silicon using the first degradation amount and the second degradation amount.

[0008] (2) The method for measuring high-temperature light-induced degradation described in (1) is as follows: In the first light soaking step, the p-type crystalline silicon is maintained at 50° C. or more and 150° C. or less for a period of 0.25 hours or more and 1000 hours or less; In the dark annealing step, the p-type crystalline silicon is heat-treated at a temperature higher than 150° C. and lower than 250° C. for a period of 5 minutes to 60 minutes, In the second light soaking step, the p-type crystalline silicon 50 The time for which the temperature is maintained at or above 150° C. may be at least 0.25 hours and at most 1000 hours.

[0009] (3) In the method for measuring high-temperature light-induced degradation according to (1) or (2), the p-type crystalline silicon may be held at 50° C. or higher and 150° C. or lower multiple times in the first light soaking step.

[0011] (4) (1)~ (3) In the method for measuring high-temperature light-induced degradation described in any one of the above, the temperature at which the p-type crystalline silicon is held in the first light soaking step may be equivalent to the temperature at which the p-type crystalline silicon is held in the second light soaking step.

[0012] (5)(4)The method for measuring high-temperature light-induced degradation described in the above item 1 includes carrying out the first light soaking step and the second light soaking step on the p-type crystalline silicon at a first temperature, carrying out the first light soaking step and the second light soaking step on the p-type crystalline silicon at a second temperature, The high-temperature light-induced deterioration amount may be calculated using the first deterioration amount and the second deterioration amount obtained at the first temperature and the first deterioration amount and the second deterioration amount obtained at the second temperature. (6) One embodiment of the method for predicting an output degradation rate of a solar cell according to the present invention includes: (1)~ (5) measuring the degradation behavior of BO-LID and LeTID of a solar cell by the method for measuring high-temperature light-induced degradation according to any one of the above; and calculating an output degradation rate of the solar cell from the measured degradation behavior of BO-LID and LeTID. Effect of the Invention

[0013] According to the present invention, it is possible to provide a method for measuring high-temperature light-induced degradation that can reliably separate the effects of BO-LID from LeTID. Also, according to the present invention, it is possible to accurately predict the aging degradation rate caused by the light degradation phenomenon of a solar cell based on the degradation behavior taking into account the temperature dependence of LeTID and BO-LID. [Brief description of the drawings]

[0014] [Figure 1] FIG. 2 is a diagram showing a method for measuring high-temperature light-induced degradation according to an embodiment of the present invention and a comparative example. [Diagram 2] FIG. 1 shows the LS-DA cycle of BO-LID. [Diagram 3] FIG. 1 shows the LS-DA cycle of LeTID. [Figure 4] FIG. 11 is a diagram showing measurement results and calculation results according to a model formula in an embodiment of the present invention. [Diagram 5]FIG. 2 is a flowchart showing a method for measuring high-temperature light-induced degradation according to an embodiment of the present invention. [Figure 6] FIG. 2 is a flowchart of a method for fitting high-temperature light-induced degradation according to an embodiment of the present invention. [Figure 7] FIG. 1 is a diagram showing a measurement device for high-temperature light-induced degradation according to an embodiment of the present invention. [Figure 8] FIG. 2 is a flowchart showing a method for predicting the degradation behavior of a BO-LID according to an embodiment of the present invention. [Figure 9] FIG. 2 is a flowchart showing a method for predicting the degradation behavior of LeTID according to an embodiment of the present invention. [Figure 10] FIG. 1 is a flowchart showing a method for predicting the output degradation rate of a solar cell from the degradation behaviors of BO-LID and LeTID according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] The method for measuring high-temperature light-induced degradation according to the embodiment of the present invention will be described below. The method for measuring high-temperature light-induced degradation according to the embodiment of the present invention has the following features. (a) a first light soaking step of injecting carriers into p-type crystalline silicon and holding the p-type crystalline silicon at a temperature of 50° C. or higher and 150° C. or lower until the p-type crystalline silicon is in a regenerated state; (b) a first measurement step of measuring a first degradation amount of the p-type crystalline silicon in the first light soaking step; (c) a dark annealing process in which the p-type crystalline silicon is heat-treated at a temperature exceeding 150°C and not exceeding 250°C; (d) a second light soaking step of injecting carriers into the p-type crystalline silicon and holding the p-type crystalline silicon at a temperature of 50° C. or higher and 150° C. or lower until the p-type crystalline silicon is in a regenerated state; (e) a second measurement step of measuring a second deterioration amount in the second light soaking step of the p-type crystalline silicon; (f) calculating an amount of high-temperature light-induced degradation of the p-type crystalline silicon using the first amount of degradation and the second amount of degradation.

[0016] (First light soaking process) The method for measuring high-temperature light-induced degradation according to this embodiment includes a first light soaking step. In the first light soaking step, a heat treatment is performed while injecting carriers into the p-type crystalline silicon until the p-type crystalline silicon is in a regenerated state. The p-type crystalline silicon is not particularly limited, and for example, p-type crystalline silicon used in solar cell modules may be used. The p-type crystalline silicon described here includes solar cells that have undergone a cell fabrication step. In other words, the method for measuring high-temperature light-induced degradation according to this embodiment may perform each step on a solar cell. Examples of carrier injection include a method of irradiating light onto p-type crystalline silicon and a method of passing a current through p-type crystalline silicon. In the light irradiation method, light having a wavelength of less than 1180 nm is used, and a current of 0.3 kW / m 2 Greater than 1kW / m 2 Greater than 3kW / m 2 In the current flow method, a voltage of more than 0.4 V, preferably more than 0.7 V, is applied. In the following description, the carrier injection is performed at a current of 1 kW / m 2 This is done by irradiating the surface with light of 10 ...

[0017] The regeneration of p-type crystalline silicon means that the minority carrier lifetime of the p-type crystalline silicon at the time of carrier injection is restored to a level equivalent to the minority carrier lifetime before the start of carrier injection into the initial state of p-type crystalline silicon. The equivalent level may be determined according to the measurement error allowed in the measurement. It is preferable that the voltage of the p-type crystalline silicon at the time of carrier injection is -2 mV or more and 2 mV or less, and further -0.5 mV or more and 0.5 mV or less, relative to the voltage of the p-type crystalline silicon before the start of carrier injection. The voltage referred to here means the open circuit voltage, hereinafter referred to as V oc The initial state refers to a state in which LeTID and BO-LID have not occurred in the p-type crystalline silicon. If the p-type crystalline silicon is not in the initial state, it is sufficient to heat treat the p-type crystalline silicon in a dark place under conditions of more than 150°C and not exceeding 250°C.

[0018] The minority carrier lifetime is the average time it takes for excess minority carriers injected into p-type crystalline silicon to recombine with majority carriers. oc It can be measured by photoconductance measurement. oc When measuring the minority carrier lifetime τ eff is the voltage to be measured, V oc As a function of, it is expressed as follows: τ eff ={n i 2 exp(qV oc / kT)} / {J ph (N AC +Δn) / qW} Here, J ph is the photocurrent density, N AC is the acceptor concentration, W is the sample thickness, n i is the intrinsic carrier concentration, q is the elementary charge, k is the Boltzmann constant, and T is the absolute temperature. The above formula is applied in a quasi-steady state. Formulas including the effects of transient states may be used. For example, the formula described in MJ Kerr, A Cuevas, “Generalized analysis of quasi-steady-state and transient decay open circuit voltage measurements”, Journal of Applied Physics 91, 399 (2002) may be used.

[0019] When measuring by photoconductance, the minority carrier lifetime τ eff is expressed as the following formula: τ eff = σ L / {J ph (μ n +μ p )} σ L is the photoconductance and J ph is the photocurrent density, and μn is the mobility of electrons, and μ p is the mobility of holes.

[0020] The lifetime may be derived using photoluminescence (PL) by using, for example, the method described in the following document: JA Giesecke, MC Schubert, D. Walter, and W. Warta, “Minority carrier lifetime in silicon wafers from quasi-steady-state photoluminescence”, Appl. Phys. Lett. 97, 092109 (2010).

[0021] V included in commercially available software oc A τ obtained from a conversion function from τ to τ may be used.

[0022] In the first light soaking step, the p-type crystalline silicon is held at 50°C or higher and 150°C or lower. The atmosphere when the p-type crystalline silicon is held may be an air atmosphere or an inert gas atmosphere such as nitrogen. This allows LeTID and BO-LID of the p-type crystalline silicon to occur simultaneously. If the holding temperature of the p-type crystalline silicon is lower than 50°C, LeTID of the p-type crystalline silicon may not occur. Therefore, it may be impossible to reliably separate the influence of BO-LID from LeTID. If the holding temperature of the p-type crystalline silicon is higher than 150°C, it may be possible to recover BO-LID. Therefore, it may be impossible to reliably separate the influence of BO-LID from LeTID. The holding temperature of the p-type crystalline silicon is preferably 65°C or higher, more preferably 80°C or higher. This allows the measurement time of high-temperature light-induced degradation to be shortened. In addition, LeTID and BO-LID can be more reliably caused. On the other hand, the holding temperature of the p-type crystalline silicon is preferably 130°C or lower, more preferably 100°C or lower.

[0023] In the first light soaking step, the p-type crystalline silicon may be held at 50°C or more and 150°C or less multiple times. In the first light soaking step, the holding time of the p-type crystalline silicon may be 0.25 hours or more and 1000 hours or less. When the holding time of the p-type crystalline silicon is 0.25 hours or more, the p-type crystalline silicon can be reliably held at the set temperature. When the holding time of the p-type crystalline silicon is 1000 hours or less, the measurement time of high-temperature light-induced degradation can be shortened. The holding time is the time for holding the p-type crystalline silicon at 50°C or more and 150°C or less. When the p-type crystalline silicon is held at 50°C or more and 150°C or less multiple times in the first light soaking step, the holding time is the time for holding the p-type crystalline silicon at 50°C or more and 150°C or less in each light soaking step.

[0024] (First measurement process) The method for measuring high-temperature light-induced degradation according to this embodiment includes a first measurement step. In the first measurement step, a first degradation amount of p-type crystalline silicon is measured. The first degradation amount is a difference between a measurement value before the first light soaking step and a measurement value at a predetermined time in the first light soaking step. The measurement value may be a minority carrier lifetime of the p-type crystalline silicon.

[0025] (Dark annealing process) The method for measuring high-temperature light-induced degradation according to the present embodiment includes a dark annealing step. In the dark annealing step, the p-type crystalline silicon that has been subjected to the first light soaking step is heat-treated at a temperature higher than 150° C. and lower than 250° C. The atmosphere during the heat treatment may be an air atmosphere or an inert gas atmosphere such as nitrogen. This allows the BO-LID of the p-type crystalline silicon to be in the state before the first light soaking step is performed. As a result, in the method for measuring high-temperature light-induced degradation according to the embodiment of the present invention, the influence of BO-LID can be reliably separated from LeTID. If the heat treatment temperature of p-type crystalline silicon is 150° C. or lower, the BO-LID of the p-type crystalline silicon cannot be reliably returned to the state before the first light soaking step is performed. As a result, in the method for measuring high-temperature light-induced degradation according to the embodiment of the present invention, it may be impossible to reliably separate the influence of BO-LID from LeTID. On the other hand, if the heat treatment temperature of p-type crystalline silicon is higher than 250° C., degradation other than LeTID and BO-LID may occur in the p-type crystalline silicon. As a result, it may be impossible to accurately measure LeTID. The heat treatment of p-type crystalline silicon is performed in a dark place. Dark annealing will hereinafter also be referred to as DA.

[0026] In the dark annealing step, the heat treatment time of the p-type crystalline silicon may be 5 minutes or more and 60 minutes or less. When the heat treatment time of the p-type crystalline silicon is 5 minutes or more, the BO-LID of the p-type crystalline silicon can be more reliably restored to the state before the first light soaking step is performed. The heat treatment time is the time for which the p-type crystalline silicon is heat treated at a temperature higher than 150°C and lower than 250°C. For example, a known heat treatment furnace may be used for the heat treatment.

[0027] (Second light soaking process) The method for measuring high-temperature light-induced degradation according to this embodiment includes a second light soaking step. In the second light soaking step, a heat treatment is performed while injecting carriers into the p-type crystalline silicon until the p-type crystalline silicon after the dark annealing step is in a regenerated state. The carrier injection can be performed in the same manner as in the first light soaking step.

[0028] The regeneration of p-type crystalline silicon means that the minority carrier lifetime of p-type crystalline silicon at the time of carrier injection is restored to a level equivalent to the minority carrier lifetime of p-type crystalline silicon before the start of carrier injection into the initial state p-type crystalline silicon. The equivalent level may be determined according to the measurement error allowed in the measurement. It is preferable that the voltage of the p-type crystalline silicon at the time of carrier injection is -2 mV or more and 2 mV or less, and further -0.5 mV or more and 0.5 mV or less, with respect to the voltage of the p-type crystalline silicon before the start of carrier injection. The p-type crystalline silicon is heat-treated in the dark annealing process. Therefore, it is considered that the BO-LID defects in the p-type crystalline silicon are in the initial state at the start of carrier injection in the second light soaking process.

[0029] In the second light soaking step, the p-type crystalline silicon is held at 50°C or higher and 150°C or lower. This allows BO-LID of the p-type crystalline silicon to occur. If the holding temperature of the p-type crystalline silicon is lower than 50°C, even if the p-type crystalline silicon is in a state in which LeTID occurs, there is a possibility that LeTID will not occur. Therefore, in the measurement method of high-temperature light-induced degradation according to the embodiment of the present invention, there is a possibility that the influence of BO-LID cannot be reliably separated from LeTID. If the holding temperature of the p-type crystalline silicon is higher than 150°C, there is a possibility that recovery of BO-LID will occur. Therefore, in the measurement method of high-temperature light-induced degradation according to the embodiment of the present invention, there is a possibility that the influence of BO-LID cannot be reliably separated from LeTID. The holding temperature of the p-type crystalline silicon is preferably 65°C or higher, and more preferably 80°C or higher. This allows the measurement time of high-temperature light-induced degradation to be shortened. On the other hand, the holding temperature of the p-type crystalline silicon is preferably 130°C or lower, and more preferably 100°C or lower.

[0030] It is more preferable that the temperature at which the p-type crystalline silicon is held in the first light soaking step is equivalent to the temperature at which the p-type crystalline silicon is held in the second light soaking step. This allows the results obtained by the BO-LID stabilization treatment to be directly compared with the results obtained by the LeTID test. As a result, the influence of BO-LID can be more reliably separated from that of LeTID. The temperature at which the p-type crystalline silicon is held in the first light soaking step is equivalent to the temperature at which the p-type crystalline silicon is held in the second light soaking step when the temperature difference is 0°C or more and 2°C or less. If the temperature at which the p-type crystalline silicon is held in the first light soaking step is not equivalent to the temperature at which the p-type crystalline silicon is held in the second light soaking step, the measurement results may be calculated to be equivalent to the temperature using a theoretical formula. As the theoretical formula, for example, the Arrhenius formula can be mentioned.

[0031] In the second light soaking step, the holding time of the p-type crystalline silicon may be 0.25 hours or more and 1000 hours or less. When the holding time of the p-type crystalline silicon is 0.25 hours or more, the p-type crystalline silicon can be reliably held at the set temperature. When the holding time of the p-type crystalline silicon is 1000 hours or less, the measurement time of high-temperature light-induced degradation can be shortened. The holding time is the time for which the p-type crystalline silicon is held at 50°C or more and 150°C or less.

[0032] (Second measurement process) The method for measuring high-temperature light-induced degradation according to this embodiment includes a second measurement step. In the second measurement step, a second degradation amount of p-type crystalline silicon is measured. The second degradation amount is a difference between a measurement value at a predetermined time in the second light soaking step and a measurement value before the second light soaking step. The measurement value may be a minority carrier lifetime of the p-type crystalline silicon. The second degradation amount is preferably the same physical quantity as the first degradation amount.

[0033] (calculation process) The method for measuring high-temperature light-induced degradation according to the present embodiment includes a calculation step. In the calculation step, the high-temperature light-induced degradation amount of p-type crystalline silicon is calculated using the first degradation amount and the second degradation amount. When the physical amounts of the first degradation amount and the second degradation amount are different, the high-temperature light-induced degradation amount may be calculated after performing a calculation to unify the physical amounts of the first degradation amount and the second degradation amount.

[0034] Next, the effects of the method for measuring high-temperature light-induced degradation according to this embodiment will be described.

[0035] Figure 2 is a diagram to explain the general principle of the LS (Light Soaking)-DA (Dark Anneal) cycle of BO-LID (Source: ACN Wenham et al., “Hydrogen-induced degradation”, Proc. IEEE 7th World Conf. Photovolt. Energy Convers., pp. 1-8, Jun. 2018.). As shown in Figure 2, initially, the BO-LID defects in p-type crystalline silicon are in STATE A. State A is a state of defect precursors that are inactive for recombination. When p-type crystalline silicon is held at a certain temperature A under carrier injection, the p-type crystalline silicon deteriorates and enters STATE B. State B is a state of defects that are active for recombination. From STATE B, when the p-type crystalline silicon is further held at a certain temperature A under carrier injection, it recovers and enters STATE C. State C is a regenerated state in which the defects are inactive. When p-type crystalline silicon in state C is heat-treated in a dark place at a prescribed temperature B, the p-type crystalline silicon returns to state A. When the p-type crystalline silicon is once again held at the prescribed temperature A under carrier injection, the p-type crystalline silicon similarly transitions to state B, and then to state C. At this time, the curve for the first LS-DA cycle and the curve for the second LS-DA cycle are almost the same. This is thought to be because, with regard to BO-LID, even if p-type crystalline silicon is heat-treated in a dark place at a temperature equal to or lower than the prescribed temperature B, a reverse reaction to the reaction that occurs at the prescribed temperature A occurs.

[0036] Figure 3 is a diagram to explain the general principle of the LeTID LS-DA cycle (Source: ACN Wenham et al., “Hydrogen-induced degradation”, Proc. IEEE 7th World Conf. Photovolt. Energy Convers., pp. 1-8, Jun. 2018.). As shown in Figure 3, when p-type crystalline silicon is held below a certain temperature C under carrier injection, the p-type crystalline silicon degrades, transitions to state B, and then to state C. Even if p-type crystalline silicon in state C is heat-treated in the dark under a certain temperature D, some of the inactivated defects in the p-type crystalline silicon do not return to state A. Furthermore, when p-type crystalline silicon is held at the certain temperature C under carrier injection again, the amount of degradation of the p-type crystalline silicon becomes smaller than the amount of degradation the first time. Furthermore, if p-type crystalline silicon is continuously held at the certain temperature C under carrier injection, the degradation width hardly changes. This is thought to be because, with regard to LeTID, even if p-type crystalline silicon is heat-treated in a dark place at a certain temperature D, the reverse reaction of the reaction that occurs at a certain temperature C does not occur.

[0037] When p-type crystalline silicon is injected with carriers and subjected to a first light soaking step in which the temperature is maintained at 50°C or higher and 150°C or lower, both LeTID and BO-LID occur. Therefore, the first degradation amount measured in the first light soaking step is considered to be the sum of LeTID and BO-LID. Furthermore, when p-type crystalline silicon is subjected to a dark annealing step in which the silicon is heat-treated at a temperature higher than 150°C and lower than 250°C, the p-type crystalline silicon undergoes a reaction with respect to BO-LID that is the opposite to that when the silicon is maintained at 50°C or higher and 150°C or lower, and the silicon returns to the state it was in before the first light soaking step was performed.

[0038] On the other hand, with regard to LeTID, even if the dark annealing process is performed, the p-type crystalline silicon does not undergo the reverse reaction compared to when the p-type crystalline silicon is held at 50°C or higher and 150°C or lower under carrier injection, and therefore does not return to the state before the first light soaking process. Therefore, when the p-type crystalline silicon is injected with carriers and then subjected to the second light soaking process in which the p-type crystalline silicon is held at 50°C or higher and 150°C or lower, only BO-LID occurs. In other words, the second degradation amount measured in the second light soaking process is considered to be BO-LID. Therefore, LeTID can be accurately quantified using the first degradation amount measured in the first light soaking process and the second degradation amount measured in the second light soaking process.

[0039] In the conventional method, the temperatures of the BO-LID stabilization treatment and the LeTID test are different. Therefore, it is difficult to directly compare the results obtained by the BO-LID stabilization treatment with those obtained by the LeTID test. As a result, it is difficult to determine whether LeTID and BO-LID have been accurately separated. On the other hand, the method for measuring high-temperature light-induced degradation according to the present embodiment can make the temperature at which the first degradation amount is measured equal to the temperature at which the second degradation amount is measured. Therefore, it becomes possible to more reliably separate the influence of BO-LID from LeTID. As a result, it is possible to more accurately quantify LeTID in p-type crystalline silicon.

[0040] (Prediction of the rate of deterioration of solar cells due to light degradation) A method for predicting the output degradation rate of a solar cell having p-type crystalline silicon from the degradation behavior of BO-LID and LeTID according to this embodiment will be described. The method for predicting the output degradation rate of a solar cell according to this embodiment may include performing the first light soaking process and the second light soaking process on the p-type crystalline silicon at a first temperature (T1) and performing the first light soaking process and the second light soaking process on the p-type crystalline silicon at a second temperature (T2) in the high-temperature light-induced degradation measurement method according to this embodiment. Then, information related to the temperature dependence of BO-LID and LeTID may be calculated using the first and second degradation amounts obtained at the first temperature (T1) and the first and second degradation amounts obtained at the second temperature (T2). This makes it possible to predict the time behavior of the BO-LID phenomenon and the time behavior of the LeTID phenomenon at any temperature in a solar cell having p-type crystalline silicon or a solar cell module having p-type crystalline silicon, and makes it possible to more accurately predict the aging degradation rate of the solar cell output.

[0041] Specifically, for BO-LID and LeTID, the reaction rate constant k AB (T1), k AB (T2) and k BC (T1), k BC (T2) is calculated, where k AB is the reaction rate constant from state A to state B, and k BC is the reaction rate constant from state B to state C. Next, for BO-LID and LeTID, k AB (T1), k AB (T2) and the Arrhenius equation to calculate the activation energy Ea(AB), and kBC(T1), k BC Calculate the activation energy Ea(BC) from (T2) and the Arrhenius equation. Furthermore, use the calculated activation energies to derive equations that give the reaction rate constants at any temperature for BO-LID and LeTID. Next, we derive an equation that gives the time change in defect density from the reaction rate equation for each of BO-LID and LeTID, and then derive an equation that gives the time change in the total defect density, which is the sum of the defect densities for BO-LID and LeTID.

[0042] Next, the relationship between the total defect density and the minority carrier lifetime, and the relationship between the minority carrier lifetime and the open circuit voltage V oc From the relationship, V oc We obtain an equation that gives the time change of V oc The time change of is the initial V oc The rate of change when normalized by V oc It can also be expressed as the time change in the deterioration rate, V oc An equation is obtained that gives the time course of the deterioration rate. Next, V oc Deterioration rate and I sc From the relationship of deterioration rate, I sc An equation is obtained that gives the time variation of the deterioration rate: where Isc is the short circuit current. Finally, V oc Deterioration rate and I sc From the equation that gives the time change in the degradation rate, we can obtain an equation that gives the time change in the Pm degradation rate of a solar cell or solar module, where Pm is the maximum output. As described above, since the reaction rate constant can be calculated at any temperature, the time change in the Pm degradation rate of a solar cell or solar cell module can also be calculated at any temperature. In other words, if the temperature of the solar cell for each hour that the solar cell operates can be given, the Pm degradation rate for each hour can be obtained. If annual temperature information is given, the annual Pm degradation rate can be calculated. The relationship between air temperature and solar cell module temperature is described in, for example, JP 2021-002988 A. In this way, the aging output degradation rate of the solar cell due to BO-LID and LeTID can be calculated.

[0043] The method for measuring high-temperature light-induced degradation and the method for predicting the output degradation rate of a solar cell according to the present invention may be implemented by computer programming.

[0044] Next, a description will be given of a high-temperature light-induced degradation measuring device according to an embodiment of the present invention. Note that the same components are designated by the same reference numerals and the description will be omitted in some cases.

[0045] As shown in FIG. 7, the high-temperature light-induced degradation measuring device 1 according to the embodiment of the present invention is characterized by including a control unit 2, a calculation unit 3, a determination unit 4, a measurement unit 5, a thermal processing unit 6, and a carrier injection unit 7.

[0046] The carrier injection unit 7 injects carriers into the p-type crystalline silicon. The carrier injection unit 7 may use a known device. The heat treatment unit 6 heat-treats the p-type crystalline silicon. The heat treatment unit 6 may use a known device. The measurement unit 5 measures the minority carrier lifetime of the p-type crystalline silicon into which carriers are injected. The determination unit 4 determines whether the p-type crystalline silicon is in a regenerated state using the minority carrier lifetime measured by the measurement unit 5. When the determination unit 4 determines that the p-type crystalline silicon is in a regenerated state, the control unit 2 controls to terminate the carrier injection and to heat-treat the p-type crystalline silicon, and controls to inject carriers into the p-type crystalline silicon after the heat treatment is completed. The calculation unit 3 calculates the amount of high-temperature-induced degradation of the p-type crystalline silicon using the minority carrier lifetime measured by the measurement unit 5. EXAMPLES

[0047] The effects of the present invention will be explained in more detail below with reference to examples. The conditions in the examples are merely examples of conditions adopted to confirm the feasibility and effects of the present invention, and the present invention is not limited to these examples. Various conditions may be adopted in the present invention as long as they do not deviate from the gist of the present invention and achieve the object of the present invention.

[0048] FIG. 5 is a diagram showing a flowchart of a method for measuring high-temperature light-induced degradation according to an embodiment of the present invention. In the embodiment, a PERC (Passivated emitter and rear contact) cell made of B-doped mono-like Si was used as p-type crystalline silicon. FIG. 1 is a diagram showing a method for measuring high-temperature light-induced degradation according to an embodiment of the present invention and a comparative example. As shown in FIG. 1, first, LS1 treatment, which is a first light soaking step, is performed on p-type crystalline silicon under 1 sun of simulated sunlight (1 kW / m 2 ) and at 95°C. At this time, the voltage of the p-type crystalline silicon was measured at sufficient time intervals for later analysis. That is, the voltage of the p-type crystalline silicon was measured using a solar simulator at predetermined time intervals from the start of the LS1 treatment. The minority carrier lifetime was calculated using the measured voltage. The LS1 treatment was performed until the minority carrier lifetime of the p-type crystalline silicon was deteriorated by LeTID and BO-LID, and the voltage was restored to the initial level, and the treatment time of the LS1 treatment was 322 hours. The voltage of the p-type crystalline silicon was determined to be in a regenerated state when it became -0.5mV or more and 0.5mV or less of the voltage before the LS1 treatment.

[0049] Next, the p-type crystalline silicon in the regenerated state was subjected to a dark annealing process, DA treatment, at 175°C for 30 minutes in a dark place. Then, the LS2 treatment, which is the second light soaking process, was performed under the conditions of 1 sun of simulated sunlight and 95°C. As with LS1, the voltage of the p-type crystalline silicon was measured at sufficient time intervals for later analysis. That is, the voltage of the p-type crystalline silicon was measured using a solar simulator at predetermined time intervals from the start of the LS2 treatment. The minority carrier lifetime was calculated using the measured voltage. The LS2 treatment was performed until the lifetime of the p-type crystalline silicon was deteriorated and then restored to the initial level, and the treatment time of the LS2 treatment was 92h. The regenerated state was judged by the same criteria as the LS1 treatment.

[0050] To confirm whether LeTID and BO-LID could be separated, the calculation results using a model formula were compared with the measurement results. In the model formula, both LeTID and BO-LID were described as a set of three-state reactions, and it was assumed that no back reaction occurs between each state. The following formulas were used for LeTID and BO-LID, respectively.

number

[0051] Next, we explain the fitting method. First, we consider the defect precursor density, N A , and the reaction rate constant k AB and k BC is used as a fit parameter, and the defect density N B When LeTID and BO-LID occur simultaneously, the lifetime change calculated from the measured values ​​does not fit well with a set of three-state models.

[0052] The fitting was performed as follows. The following τ and V oc Using the relation, V oc (t) to τ(t). τ eff ={n i 2 exp(qV oc / kT)} / {J ph (N AC +Δn) / qW} The measured lifetime τ(t) at time t during the LS process and the reference time t that does not contain any defects 0 Measured lifetime τ(t 0) was used to obtain the normalized defect density (NDD) at time t during LS processing. NDD=1 / (τ(t))-1 / τ(t 0 ) In this case, if the sample contains defects in the initial state before the LS process, the NDD after recovery will be negative. For fitting purposes, a constant was added to NDD(t) to correct the NDD so that the minimum value would be 0. The fitting was performed in the following manner. eff and V oc Using the relation, V oc (t) to τ(t). τ eff ={n i 2 exp(qV oc / kT)} / {J ph (N AC +Δn) / qW} The measured lifetime τ(t) at time t during the LS process and the reference time t that does not contain any defects 0 Measured lifetime τ(t 0 ) was used to obtain the normalized defect density (NDD) at time t during LS processing. NDD = 1 / (τ eff (t))-1 / τ eff (t 0 ) In this case, if the sample contains defects in the initial state before LS processing, the NDD after regeneration will be negative, so for fitting purposes, a constant was added to NDD(t) to correct it so that the minimum value of NDD becomes 0. Using the reaction model described above, N A , k AB , k BC When the differential equation in Eq. (1) is solved with the fit parameters, the number of defects in the recombination-active state, N B Fitting was performed to minimize the difference between (t) and the corrected NDD(t).

[0053] V oc was calculated from the fit parameters in the following way:A , k AB , k BC Use N B was calculated. If the fitting is good, N B The NDD can be regarded as a normalized defect density (NDD) corrected by subtracting the constant added during the correction to obtain the original NDD. 0 The reciprocal of the minority carrier lifetime measured at 1 / τ eff (t 0 ) and τ eff (t) is obtained. V oc From τ eff Using the formula used to convert to (t), oc Using the fit parameters for the data in the case where BO-LID is dominant, the obtained V oc is the V affected by BO-LID at temperature T oc The method for calculating the fitting parameters is shown in Figure 6.

[0054] On the other hand, if p-type crystalline silicon is subjected to sufficient LS1 and DA treatments, the reservoir state of LeTID changes sequentially from a defect precursor state to a defect state and then to a regenerated state. It is believed that the reservoir state will eventually be exhausted and the entire state will be regenerated. If DA treatment is performed on p-type crystalline silicon at the stage where the entire state is regenerated, LeTID will not occur because the reservoir state has been exhausted, and only BO-LID will occur.

[0055] Therefore, when fitting the minority carrier lifetime change calculated from the measurements in the LS2 process after the DA process using a set of three-state models, since only BO-LID occurs, the minority carrier lifetime change fits well with only a set of three-state models. If the minority carrier lifetime change in the LS2 process does not fit sufficiently, perform the DA and LS processes again until the LeTID reservoir state is depleted. This allows the effect of BO-LID to be understood.

[0056] LeTID and BO-LID can be separated by subtracting the minority carrier lifetime change when only BO-LID occurs from the lifetime change when LeTID and BO-LID occur simultaneously. Whether LeTID and BO-LID have been separated can be judged by whether the subtracted lifetime change can be well fitted by a set of three-state models.

[0057] The voltage V when LS1 was performed for 322 hours at 1 sun / 95℃ for p-type crystalline silicon oc The change in V is shown in Fig. 4(a). Also, V was calculated using the parameters obtained from the fitting with the three-state model without back reaction. oc The solid line shows the change in N B Therefore, the solid line in Figure 4 is the fitted N B V calculated using oc In this fitting, the actual V oc The fit is not very good with the change in . The fit was judged to be good enough using the normalized root mean squared error (RMSE). The smallest normalized RMSE for this fit was 0.115.

[0058] For p-type crystalline silicon, after LS1 treatment, DA treatment was performed at 175°C for 30 minutes, and then LS2 treatment was performed again at 1 sun / 95°C for 92 hours. oc The change in V is shown in Fig. 4(b). The fitting result is also shown by the solid line. The three-state model without back reaction is oc Therefore, the deterioration and recovery behavior in LS2 is considered to be due to BO-LID.

[0059] Next, the results of the LS2 process and the BO-LID effect calculated on the same time scale as LS1 are shown in Figure 4(c). ocThe black squares show the results (LS1-LS2) obtained by subtracting the effect of BO-LID from the above (white circles in Fig. 4(c)). Figure 4(d) shows the results of fitting to LS1-LS2. Figure 4(d) shows a better fit than Fig. 4(a). Therefore, it is believed that LeTID and BO-LID were able to be separated. The minimum normalized RMSE in the fit was used to determine whether the fit was sufficient. The normalized RMSE was 0.0689.

[0060] 8, 9 and 10 are flowcharts showing a method for predicting the output degradation rate of a solar cell from the degradation behaviors of BO-LID and LeTID according to an embodiment of the present invention. Next, the reaction rate constants k for BO-LID and LeTID obtained by performing the above-mentioned light soaking test at two temperatures (the first temperature T1 and the second temperature T2) are AB (T1), k AB (T2), k BC (T1), k BC Based on (T2), a method for predicting the aging degradation rate caused by BO-LID and LeTID of a solar cell module will be described with reference to the flowcharts shown in Figures 8, 9, and 10. Figure 8 shows the flow until an equation that gives the time change considering the temperature dependency of BO-LID is derived, and Figure 9 shows the flow until an equation that gives the time change considering the temperature dependency of LeTID is derived. And Figure 10 shows the flow until an equation that predicts the output degradation rate caused by BO-LID and LeTID of a solar cell module is derived based on the equations derived in the steps shown in Figures 8 and 9.

[0061] The procedure for deriving an equation that gives the time change taking into account the temperature dependency of BO-LID will be described below with reference to FIG. First, in Step 1, the reaction rate constant k was calculated from the light soaking test results at two temperatures (T1, T2). AB (T1), k AB (T2), k BC (T1), k BC Obtain (T2). Next, as Step 2, kAB (T1) and k AB (T2), and calculate the activation energy Ea(AB) from equation (1)-a and equation (2-a), k BC (T1) and k BC Calculate the activation energy Ea(BC) from (T2) and equations (3)-a and (4)-a. Next, in Step 3, the activation energy Ea(AB) and the constant k, which is the coefficient of the reaction rate constant from equation (1-a), are calculated. AB 0, and similarly, from the activation energy Ea(BC) and equation (3-a), the constant k BC Find 0. Next, in Step 4, the activation energy Ea and the coefficient of the reaction rate constant obtained in Step 3 are used to calculate the reaction rate constant k at any temperature T. AB (T) and k BC Equations (5)-a and (6)-a which give (T) are obtained.

[0062] Next, in Step 5, the defect density (N A , N B , N C ) are expressed as the partial differential equations (7)-a, (8)-a, and (9)-a, respectively, by applying the reaction rate constant k obtained in Step 4. AB (T) and k BC Substitute (T). Next, in Step 6, the partial differential equation for time given in Step 5 is replaced with a difference equation for time, and the infinitesimal increase in defect density ΔN (ΔN A , ΔN B , ΔN C ) to obtain the formula ΔN A For equation (10)-a, ΔN B For equation (11)-a, ΔN C is given by equation (12)-a. If we consider a situation where the time transition is expressed by continuously giving it in units of minute time Δt, then N B (t) BO-LIDThe increment from the initial value can be calculated using equation (13)-a. Note that i in equation (13)-a indicates the i-th time when the time unit is Δt. Using Fig. 8, we have calculated the time behavior of the defect density N B (t)The procedure for deriving the formula for BO-LID has been explained. The time behavior of defect density N B (t) LeTID In the case of deriving an equation that gives the above equation, equation (13)-b can be obtained in a similar manner, as shown in FIG.

[0063] The explanation will be continued with reference to FIG. 10. Next, in Step 7, N B (t) BO-LID and N B (t) LeTID By adding up the total defect density N B (t) Total Then, by using equation (15), we obtain the total defect density N B (t) Total and minority carrier lifetime τ eff (t). In general, the relationship between defect density N and minority carrier lifetime τ is given by N=1 / {σ·v th ·τ}, where σ represents the capture cross section of the minority carriers, and v th represents the thermal velocity of minority carriers. Equation (15) expresses the initial lifetime τ eff (0) and lifetime τ after light exposure t hours eff This equation relates the difference in (t) to the sum of the increment in defect density that gives BO-LID and the increment in defect density that gives LeTID after t hours of light irradiation. By rearranging equation (15), we obtain τ eff We obtain equation (16) which expresses (t). Next, in Step 8, we use equation (17) to calculate the minority carrier lifetime τ eff and open circuit voltage V oc By relating and transforming this, V oc Time behavior of V ocWe obtain equation (18) which expresses (t).

[0064] Next, Step 9: V oc (t) is the initial V oc The rate of change when normalized by V oc Re-expressing it in terms of the degradation rate (t) gives equation (19). Next, V obtained as a result of the light irradiation test is oc Deterioration rate and I sc Using equation (20) which expresses the correlation between deterioration rates, I sc The deterioration rate (t) is expressed by equation (21). Here, the coefficients in relational equation (20) vary depending on the substrate type, element structure, etc., and are not universal values. It is desirable to obtain relational equation (20) according to the substrate type, element structure, etc. Finally, as Step 10, V oc Deterioration rate (t) and I sc Adding the deterioration rate (t), we obtain equation (22) which gives the Pm deterioration rate (t). As a result of the above, it is possible to obtain the time behavior that takes into account the temperature dependency of the output degradation rate of a solar cell module caused by BO-LID and LeTID. For example, if annual transition information of the solar cell module temperature is given, it is possible to predict the annual Pm degradation rate caused by BO-LID and LeTID. If the annual Pm degradation rate prediction is performed for each year following the first year, it is possible to predict the aging Pm degradation rate caused by BO-LID and LeTID.

[0065] Regarding the air temperature and the temperature of the solar cell module, the following relationship is known to hold as a guideline: Here, the unit of temperature is [°C], NOCT is the nominal operating cell temperature, and S is the amount of incident sunlight [mW / cm 2 The NOCT may be one specified in the solar cell manufacturer's specifications. Solar cell module temperature = air temperature + ΔT ΔT=(NOCT-20)×S / 80

[0066] In addition, when it is difficult to obtain the time transition information of S, the defect increase amount ΔN due to photodegradation per day can be expressed as follows using the daily maximum temperature Tmax and the effective stress time heff. Here, heff is in the same unit as the time unit Δt. Also, ΔN is ΔN B The following case will be described as an example. Daily maximum module temperature Tmp = Daily maximum air temperature Tmax + ΔT ΔT=25℃ (guideline for ground installation), 35℃ (guideline for residential roof installation) ΔN per day B ≒(k AB (Tmp)×N A -k BC (Tmp)×N B ) ×heff

[0067] ΔN per day above B If you add it up for 365 days a year, you get ΔN per year. B We can calculate ΔN for each year following the first year. B can be calculated in the same way. ΔN B As mentioned above, if the time behavior of can be calculated, the time behavior of the Pm degradation rate of the solar cell module can be calculated. It is known that photodegradation of solar cell modules occurs in the form of degradation and recovery over a period of one year (for example, degradation in summer and recovery in winter), and furthermore, the phenomenon of this degradation and recovery phenomenon repeating every year after the first year is also known. It is believed that similar behavior occurs in BO-LID and LeTID, which are representative photodegradation phenomena. In order to make it possible to predict the time behavior of the Pm degradation rate of solar cell modules taking this phenomenon into consideration, for example, in the procedure of sequentially calculating each defect density as time progresses, an operation can be performed in which NA, which is the defect precursor density, is reset to a predetermined value (for example, the initial value) after a predetermined time has passed (for example, in winter). Alternatively, N B Reduce by a certain amount and put the reduced amount into N AThe selection of these operations and the adjustment of the predetermined values ​​can be made based on the results of outdoor exposure tests or the results of light irradiation tests in which the temperature is changed over time to simulate outdoor exposure tests.

[0068] We have specifically explained how to predict the output degradation rate of solar cells from the degradation behavior of BO-LID and LeTID. Predicting the aging Pm degradation rate is essential for predicting the power generation amount of solar cell modules and calculating the power generation cost [yen / kWh], and is extremely important industrially.

[0069] Throughout the specification, when a part is described as "having" or "comprising" a certain element, this does not mean that it excludes other elements, but that it may further include other elements, unless specifically stated to the contrary.

[0070] Furthermore, the term "part" used in the specification means a unit that processes at least one function or operation, which may be embodied as hardware or software, or as a combination of hardware and software.

[0071] In addition, the components in the above-described embodiment may be replaced with known components as appropriate without departing from the spirit of the present invention. In addition, the above-described modified examples may be combined as appropriate. For example, Czochralski silicon (Cz-Si), floating zone silicon (FZ-Si), multicrystalline silicon (mc-Si), and mono-like silicon may be used as the substrate. [Industrial Applicability]

[0072] As described above, the present invention provides a method and device for measuring high-temperature light-induced degradation that can reliably separate the effects of BO-LID from LeTID, and is therefore highly industrially useful. In addition, the present invention can accurately predict the aging degradation rate of solar cells caused by the light degradation phenomenon based on the degradation behavior that takes into account the temperature dependence of LeTID and BO-LID, and is therefore highly industrially useful.

Claims

1. a first light soaking step of injecting carriers into the p-type crystalline silicon and maintaining the p-type crystalline silicon at a temperature of 50° C. or higher and 150° C. or lower until the p-type crystalline silicon is in a regenerated state; a first measurement step of measuring a first deterioration amount of the p-type crystalline silicon in the first light soaking step; a dark annealing step of heat-treating the p-type crystalline silicon at a temperature higher than 150° C. and lower than 250° C.; a second light soaking step of injecting carriers into the p-type crystalline silicon and holding the p-type crystalline silicon at 50° C. or higher and 150° C. or lower until the p-type crystalline silicon is in a regenerated state; a second measurement step of measuring a second deterioration amount of the p-type crystalline silicon in the second light soaking step; A calculation step of calculating a high-temperature light-induced deterioration amount of the p-type crystalline silicon using the first deterioration amount and the second deterioration amount. A method for measuring high-temperature light-induced degradation.

2. In the first light soaking step, the p-type crystalline silicon is maintained at 50° C. or more and 150° C. or less for a period of 0.25 hours or more and 1000 hours or less; In the dark annealing step, the p-type crystalline silicon is heat-treated at a temperature higher than 150° C. and lower than 250° C. for a period of time of 5 minutes to 60 minutes, In the second light soaking step, the p-type crystalline silicon is kept at 50° C. to 150° C. for 0.25 hours to 1000 hours.

2. The method for measuring high-temperature light-induced degradation according to claim 1.

3. In the first light soaking step, the p-type crystalline silicon is kept at 50° C. or more and 150° C. or less for a plurality of times.

3. The method for measuring high-temperature light-induced degradation according to claim 1 or 2.

4. The temperature at which the p-type crystalline silicon is held in the first light soaking step is equal to the temperature at which the p-type crystalline silicon is held in the second light soaking step. The method for measuring high-temperature light-induced degradation according to any one of claims 1 to 3.

5. performing the first light soaking step and the second light soaking step on the p-type crystalline silicon at a first temperature; subjecting the p-type crystalline silicon to the first light soaking step and the second light soaking step at a second temperature; The high-temperature light-induced deterioration amount is calculated using the first deterioration amount and the second deterioration amount obtained at the first temperature and the first deterioration amount and the second deterioration amount obtained at the second temperature.

5. The method for measuring high-temperature light-induced degradation according to claim 4.

6. A method for measuring high-temperature light-induced degradation according to any one of claims 1 to 5, comprising the steps of: measuring the degradation behavior of BO-LID and LeTID of a p-type crystalline silicon solar cell; and calculating an output deterioration rate of the solar cell from the measured deterioration behavior of BO-LID and LeTID. A method for predicting the rate of output degradation of solar cells.

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